(1) Field of the Invention
The invention relates to an apparatus for producing a holding and/or traversing frame for a stacked piezoactuator that contributes to increasing the piezopath. Moreover, the invention relates to an electrostrictive drive with such a holding and/or traversing frame.
(2) Description of Related Art
For activation of flaps in, for example, a helicopter rotor or other applications in aviation, piezoactuators or electrostrictive actuators are known to be used. In particular, stacked piezoactuators that are also called piezostacks are used that expand when an electrical voltage is applied and thus make available an adjustment path. Since, however, in, for example, a stacked piezoactuator with a length of 100 mm the possible expansion, i.e., the adjustment path, is approximately in the range of 0.1 mm, it is desirable to enlarge the piezopath by means of a traversing mechanism, for example, by a factor of 10 or the like. For this purpose, placing and clamping the electrostrictive actuator, especially the piezostack, in a traversing frame that makes available a path of the activated piezoelement that has been increased by the traversing factor in a direction perpendicular to the piezopath, i.e., perpendicular to the change in the length of the piezoelement, are known.
Such a frame that is shaped essentially octagonally is known, for example, from DE 197 39 594 A1. The frame consists of rigid, metal frame parts that are connected to one another via flexible articulation sites. There are four fixed frame parts. The articulation sites are each formed from several elastic bending elements that lie on top of one another with bending joint axes parallel to one another and on one side are connected to a fixed frame part that connects all the bending elements of the articulation site integrally to one another. The other fixed frame part that is connected to the articulation site is divided into several separate individual levers that are each connected to a bending element of the articulation site. The frame parts are made integrally solid.
DE 196 25 921 A1 discloses an arrangement in which the metallic frame parts of the above-described prior art are replaced essentially by bending-flexible tie rod parts that are, however, highly stiff in the lengthwise direction. The tie rod parts are formed from pieces of steel cable or a fiber composite laminate with a lengthwise fiber structure that is unidirectional in the lengthwise direction of the rod and are provided as necessary with reinforcing elements that increase the tensile strength on their middle regions located between the actuator pieces and output members.
Another piezoelectric actuator is known from DE 196 44 161 C2, in which there are at least two disk-shaped bending elements that are located coaxially on top of one another and that each have a carrier plate of hard elastic material with a layer of piezoelectric material applied on one or both sides. Two bending elements at a time are connected to one another via at least two bending joints located on the periphery of the carrier plates, such a bending joint having at least one bending beam and a rigid spacer piece that is essentially perpendicular to it.
So that the traversing frame can work reliably, it is necessary for the four frame legs that form such an essentially octagonal frame to have tensile stiffness and to be at the same time very flexurally soft in the joints. Moreover, it is necessary for them to tolerate continuous loads at high frequencies, for example on the order of magnitude of 30 Hz, and, moreover, to have, as much as possible, such slow damage progression in case of damage that sudden total failure cannot occur. Rather, damage that arises and leads to failure should be able to be discovered within the prescribed inspection intervals. This is especially important in safety-relevant applications, such as, for example, in applications of such an electrostrictive actuator for flap control of a helicopter rotor.